1. Field of the invention
The invention relates to a connection device for the mechanical and electric connection of well probes to an electric suspension cable.
2. Description of the Prior Art
Measurements in boreholes are made by means of sensors contained generally in one or more probes lowered from a surface installation at the end of an electric suspension cable capable of supporting the weight of the probes and formed of a plurality of electric conductors. One of the probes at least has anchorage arms actuated by jacks. The liquid required for operating the jacks is produced by a hydraulic system generally driven by an electric motor fed from a surface installation via electric conductors of the cable.
Operation of the anchorage arms for immobilizing the probe (or the probes) at a given depth in the well or borehole is controlled by means of solenoid valves connected by one or more conductors to the surface installation. Other electric conductors are used for connecting different sensors contained in the probes to a recording laboratory and in particular the different sensors used for determining the characteristics of the formations of the sub-soil surrounding the borehole.
The requirements of seismic prospection by which it is desired to obtain as rapidly as possible detailed recordings of the seismic profiles lead to using a greater and greater number of sensors and distributing them in an assembly of probes suspended below each other. The different signals from the different sensors are collected by a data acquisition apparatus designed for multiplexing, digitizing and adapting these signals before transmitting them to one or more lines of the cable to the surface seismic laboratory. The data acquisition is coordinated from the seismic laboratory which sends control and synchronization signals to the reception device in the well. The connection of each sensor disposed in a satellite probe with the data acquisition apparatus disposed generally in the main probe is provided by a special conductor.
The different parts of such a spread cable are described for example in the following French patent application Nos.: FR-2 501 380, 2 548 727, 2 564 599, EN 87/04 365 and EN 87/04 677.
The construction of a spread cable thus formed of a set of several probes spaced apart at different depth levels and containing a large number of sensors makes it then necessary to provide a large number of connections not only between the surface recording and control laboratory and the main probe but also between this latter and the different satellite probes.
It is thus necessary to provide electric connectors which are more and more complex for connecting the different probes to the connection cables.
The construction of such connections is all the more delicate since the probes, for the needs of seismic prospection particularly, must be lowered to depths of several kilometers where pressures prevail of several hundred bars and temperatures which may reach 200.degree. to 300.degree. C.
The connection of the cable to the end of the probes is generally provided by means of a sealed passage element formed of a thick dividing wall in the form of a disk made from in insulating material through which pass metal rods extending on each side of the dividing wall.
The rods are welded or crimped on one side to the conductors of the cable and on the opposite side to the conductors inside the probe. The connection zone is defined and isolated, on each side of the dividing wall, by means of a sleeve formed of two half shells brought together so as to grip the cable and the end of the body of the probe and are fixed together.
Seals are disposed between the two half sheels for isolating this cavity and an insulating substance is injected therein. In order to make the connection between the cable and the different conductors inside each probe removable, a multi-pin electric connector is further used disposed in the cavity on one side of the dividing wall. The construction of each interconnection is time-consuming and difficult for this reason. Furthermore, the electric insulation is difficult to maintain when the external hydrostatic pressure becomes very high because of the method of confining the conductors by means of half shells, which do not withstand the entry of water.
The device of the invention overcomes the above drawbacks. It includes electric connection means providing the connection between different electric conductors in the probe and conductors of the multi-conductor cable, and mechanical fixing means for fixing the cable to the end of the well-probe.